1. Technical Field of the Invention
This invention relates to magnetic recording media and, particularly, a flexible magnetic recording sheet stretched across a rigid, disk-shaped support to provide a planar recording surface.
2. Description of the Prior Art
Conventional, commercially available linear tape recording systems have excellent fidelity characteristics, are durable and are relatively inexpensive. The main shortcoming of linear tape systems is that access to different portions of the tape requires a relatively large amount of time.
A disk configuration, on the other hand, will allow random access to different portions of the magnetically recorded material since all of the material is available on one plane. In addition, a plurality of magnetic transducer heads may be used in conjunction with a disk to provide rapid access to random portions of the material recorded on the disk.
One type of recording disk configuration presently in wide-spread use is the so-called "floppy" disk, such as illustrated in Flores et al. U.S. Pat. No. 3,668,658. This disk type consists of a relatively thick sheet of polymeric material which includes a magnetizable surface coating. Floppy disks are both inexpensive and convenient to use. Drawbacks associated with this type of disk, however, are that the disk experiences relatively large dimensional changes in response to temperature and humidity fluctuation and that a pressure pad opposite the head is required which causes wear, limits the rotational speed and, hence, reduces access times.
Stretched surface recording (SSR) disks are shown in U.S. Pat. Nos. 2,662,804 (Hutton); 3,130,110 (Schmidt); 3,336,583,(Comstock); 3,373,413 (Treseder); 3,488,646 (Sugaya); 3,509,274 (Kihara); 3,537,083 (Voth); 3,599,226 (Lips); and German Offenlegungsschrift No. 2,342,890 (Boissevain). The SSR disks described in the foregoing patents typically include a concave base having a rim across which is stretched a polymeric sheet, such as polyethylene terephthalate polymer (Mylar), coated with iron oxide. This type of disk is superior to floppy disks in that a pressure pad is not required and the recording surface has substantially the same dimensional stability as the relatively massive base to which it is attached. In addition, the SSR disk provides an extremely flat recording surface which may be deformed slightly to conform to a transducer head and irregularities in the surface of the head.
In spite of the advantages of SSR disks over floppy disks, SSR disks have not been commercially successful, perhaps because of production costs and the difficulty of producing a consistent tensioned surface in a production setting.
The success and utility of an SSR disk depend upon maintaining the recording surface in a tensioned condition across the rim of the support and reliably attaching the recording film to the support. It has been difficult in a production setting to adequately and uniformly tension the recording surface without using elaborate and expensive equipment and fixturing, and it has been difficult to reliably attach the recording surface to the support because of the inherent difficulties in attaching a very thin sheet to a relatively massive object without damaging the sheet.